Link collection from external .blend in 2.8 via python
Thanks for your initial self-answer! It got me on the right track.

I think this way is even easier:

import bpy

master_collection = bpy.context.scene.collection

blendFile = 'path/to/file.blend'

with bpy.data.libraries.load(blendFile) as (data_from, data_to):
    data_to.collections = data_from.collections


for new_coll in data_to.collections:
    instance = bpy.data.objects.new(new_coll.name, None)
    instance.instance_type = 'COLLECTION'
    instance.instance_collection = new_coll
    master_collection.objects.link(instance)